The invention relates to a fluid pump for a motor vehicle, for example a water pump for circulating coolant.
Water pumps for circulating the coolant of the engine are used in motor vehicles. The shaft of such a water pump, to which the pump rotor is fastened, is generally connected to the engine via a toothed belt or V-ribbed belt; thus enabling coolant to be pumped at the same time that the engine is operating.
The circulation of the coolant can be optimized with a switchable water pump, i.e. a water pump in which the pump output can be adjusted. On the one hand, the heat-up behavior of the engine can, for example, be accelerated by means of a deactivated or stationary water pump in the warm-up phase of the engine; and on the other hand, the power dissipation of the water pump can be reduced.
An electromagnetic clutch can, for example, be used for connecting and separating the pump shaft from the pump rotor. In so doing, churning losses due to decoupling can be prevented; however, relatively high magnetic forces are normally required in order to be able to ensure the frictional connection of the clutch in all circumstances, which can lead to a large use of and expenditure for copper.
In addition, there are water pumps comprising a switchable friction wheel clutch comprising a switchable intermediate wheel, in which the length of the tensioning arm can be electrically adjusted by means of an eccentric. Due to environmental influences on the engine, a frictionally engaged transmission is however not very robust.
A hydraulically actuated control gate valve is also used to close the outlet region of the pump rotor and thereby deactivate the pump. In so doing, the rotor continues to rotate at an unchanged rotational speed and generates churning losses in the coolant.
A further switching principle is based on a pump rotor comprising guide vanes that can be rotated coaxially to the rotor inlet, which, however, again leads to churning losses.